Differential pinion, metal mold for plastic working the same, and method for plastic working with the metal mold

Abstract

The present invention relates to a differential pinion for automobiles or the like, a metal mold for plastic working the differential pinion, and a method for plastic working with the above metal mold. And particularly the differential pinion of the present invention is provided with an end relief section which is effective to reduce a noise and has a continuous fiber flow from a tooth face to the end relief section providing a high pitting resistance. The metal mold for plastic working the differential pinion of the present invention can provide the internal pressure working area of the die in a position deep below the open end by a required distance therefrom, thereby providing the metal mold with higher rigidity and strength. Further, in the plastic working method of the present invention, it is very easy to position the punch under pressure stress in the axial direction.

What is claimed is: 
     
       1. A metal mold for plastic working a differential pinion having a plurality of teeth, wherein each tooth comprises an uncut, unground end relief face intersecting with a cone distance large end face and a tooth face, the tooth face and the end relief face each having continuous fiber flow, the fibers being longitudinally aligned in such manner that they are parallel to the tooth face and the end relief face substantially at all points therealong, to thereby improve tooth contact and reduce noise and pitting of the teeth without requiring grinding or cutting the pinion after forming thereof, the metal mold has a punch fitted with a die and the punch has its portion facing the die formed with a shape corresponding to said cone distance large end face and the die has a first space and a second space, wherein the first space is on the side of a cone vertex with a face as a boundary for producing a certain tooth shape and the second space is bounded by a die surface parallel to an axis of rotation of the differential pinion, said die surface forming said end relief face, and said second space continues to an open end of the die facing the punch, wherein the punch is fitted in said second space and guided by said die surface. 
     
     
       2. A method for plastic working with the plastic working metal mold for the differential pinion of claim 1, comprising the step of: inserting the portion of the punch facing the die to a desired cone distance large end face position in the die to produce the tooth face, the end relief face and the cone distance large end face simultaneously.